Disclosed is a method for the disintegration of lignocellulosic materials to fibers and a method for further processing these fibers.
Before lignocelluloses are processed into engineering and insulating materials, reinforcing or filler materials, cardboard or fuels they are typically comminuted into either shavings or fibers. The thin and usually arcuate fibers are increasingly winning out economically over the straight, stiff and strongly resilient shavings since they have better processing properties and the products produced therewith are of higher value.
The most widely used machines for defiberizing the lignocelluloses are grindstones, twin-screw extruders and also conical or disk refiners. Currently, it is the twin-disk refiners which dominate. In the twin-disk refiner, the defiberizing disintegration mainly takes place as a result of shearing stress exposure between the two parallel grinding disks which are profiled on their inside surfaces with ribs and of which one is mounted rigid and the other rotates at high speed. In the course of the disintegration process, the lignocelluloses stream radially as an aqueous flowable mass into the refiner and exit therefrom through the increasingly narrowing gap between the grinding disks. During the process, the lignocelluloses are gradually split open by shearing forces to form fibers of high to very high fineness.
Disadvantages of the defiberization machines mentioned include low throughput rates and/or high electrical energy requirements. The currently dominating refiner process moreover has the disadvantage that the defiberization of comparatively hard lignocelluloses, such as wood for example, only becomes possible once the raw material has been hydrothermally softened beforehand by a cooking process at high pressures of about 10 to 20 bar and temperatures of about 160 to 220° C. This is typically done with expensive equipment and significant thermal energy. Furthermore, the dewatering of the fibrous pulp generates large amounts of dirty wastewater.
The disintegration of lignocelluloses by means of refiners gives rise to fibers which are not very enhanced on the inside, since the defiberization process mainly involves the application of shearing stress. Therefore, the high porosity in the fibers is largely retained. In addition, admixed substances, such as binding and/or hydrophobicizing agents for example, become mainly dispersed on the surface of the fibers. The pore volume of the fibers contains gases, once the water has dried off. The pores in the fibers reduce the strength of the fibers and they compromise the compression characteristics of the fiber in the production of fiber base materials by pressing for example, since the gases enclosed in the pores increase the resistance to compression and reinforce the reexpansion after the pressure applied has been removed from the compressed material. The latter can even lead to the material being destroyed by expansion cracks.
The pore volume can also lead to product damage through the ingress of water and/or of microorganisms.
Within the context of the production of novel engineering materials based on lignocellulose, the disclosure provides a method for the disintegration of lignocelluloses having improved and also flexibly adjustable properties, which utilizes a low number of process stages and also low levels of thermal and electric energy, and which does not generate dirty wastewaters from a cooking process.